Photocurable resin compositions that are cured by UV lights or electron beams have a short curing time and are advantageous over thermosetting resin compositions in terms of such aspects as resource saving, energy saving and high productivity, thus finding use in a wide range of applications such as inks, paints, coating agents, hard coats, films, adhesives, pressure sensitive adhesives, surface processing agents, lenses, resists, polarizers, sealants, liquid crystals, dental materials and nail cosmetics. Acrylates and methacrylates are widely used in such photocurable resin compositions because of their good curability.
The curable resin compositions sometimes contain triacrylate monomers, trimethacrylate monomers and the like as crosslinking agents or reactive diluents. Some of such triacrylate monomers are trimethylolpropane triacrylate, alkylene oxide-modified trimethylolpropane triacrylate, ditrimethylolpropane triacrylate, alkylene oxide-modified ditrimethylolpropane triacrylate, pentaerythritol triacrylate, alkylene oxide-modified pentaerythritol triacrylate, isocyanurate triacrylate, alkylene oxide-modified isocyanurate triacrylate, glycerol triacrylate and alkylene oxide-modified glycerol triacrylate.
Some example trimethacrylates are those corresponding to the above acrylates except that the acrylate moiety is replaced by methacrylate, namely, trimethylolpropane trimethacrylate, alkylene oxide-modified trimethylolpropane trimethacrylate, ditrimethylolpropane trimethacrylate, alkylene oxide-modified ditrimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, alkylene oxide-modified pentaerythritol trimethacrylate, isocyanurate trimethacrylate, alkylene oxide-modified isocyanurate trimethacrylate, glycerol trimethacrylate and alkylene oxide-modified glycerol trimethacrylate.
These monomers that are generally used, such as trimethylolpropane triacrylate, have high curing shrinkage and thus often come with problems such as cracks during curing, decreased flexibility and curls. To decrease the curing shrinkage or to reduce skin irritancy, the raw material triols are sometimes modified with alkylene oxides and then acrylated. This approach, however, often results in a decrease in curability or crosslinking density by the extension of chain length. Further, extended chains can also cause the viscosity to be increased or the adhesion and weather resistance to be decreased (see, for example, Japanese Patent Application Kokai Publication No. H6-271623; and Kunihiro Ichimura, Dai 5 sho (Chapter 5) Rajikaru jugokei monoma origoma (Radical polymerizable monomers and oligomers), UV kohka no kiso to jissen (Foundation and practice of UV curing), Yoneda Shuppan (Yoneda Publishing), issued Oct. 7, 2010, pp. 55-69). Furthermore, such an alkylene oxide-modified product cannot be obtained as a single compound due to the difficult control of the number of alkylene oxide molecules added, and also tends to be in the form of a peroxide because of having a large number of primary ether bonds and can cause gelation at times.
Thus, there has been a demand for triacrylate compounds as monomers that are balanced in properties such as low curing shrinkage, flexibility, flex resistance, low curling properties, adhesion and curability.